ConsumerGroupMetadata is internal and there is no (clean) way for an external library to wrap it

IConsumerGroupMetadata is an empty interface, that does not have a public property/method to access the metadata itself, while ConsumerGroupMetadata has an internal field containing the serialized version of metadata.

https://github.com/confluentinc/confluent-kafka-dotnet/blob/2b54dd2ab07f6eaa886d88c57143838627b2512f/src/Confluent.Kafka/ConsumerGroupMetadata.cs#L23

Due to this design, the only way to get metadata of a consumer group is to cast IConsumerGroupMetadata to ConsumerGroupMetadata.

https://github.com/confluentinc/confluent-kafka-dotnet/blob/2b54dd2ab07f6eaa886d88c57143838627b2512f/src/Confluent.Kafka/Impl/SafeKafkaHandle.cs#L553

A better way to do it would be to have a public property to get metadata as byte[] in IConsumerGroupMetadata itself. Please, consider this change.

P.S. I will try to do these changes in my free time, but maybe there is a samaritan that could do this now.

[agayev169]

@agayev169 The ConsumerGroupMetadata’s purpose is to pass consumer group state from a consumer to a transactional producer, the state information is of no use to the application and thus there’s no reason to expose it.

I get your point, and partially agree with you on this point; however, let’s consider my case. I am trying to develop a service using Kafka. I do not want to leave Kafka dependencies in the public API of the service (maybe it will be change in the future, who knows), so I tried to wrap all the components that I need under my own public API (consumer, producer, message, etc.). The only problem that I faced till now is that I cannot wrap the ICosumerGroupMetadata since it does not let me get the metadata itself from my service (both ConsumerGroupMetadata and variable storing metadata are internal).

So, what I find missing is a public method that would let me get the metadata as byte[].

[mhowlett]

the java client actually exposes information on the instance returned from groupMetadata, which is what is passed to the transactional producer. whether on not this is really useful (seems like @agayev169 want’s it), our api does expose less than the Java one does.